JPH1049858A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a magnetic a magnetic recording medium by which a good electromagnetic conversion characteristic is obtained in a high-density recording region by making an upper-layer magnetic layer contain at least either a surface-active agent or the organic amine salt of a surface-active agent. SOLUTION: When a surface-active agent is contained in the upper-layer magnetic layer 3, hydroxyl group of the surface-active agent and the surface of a metal magnetic powder mutually act, and the surface-active agent is adsorbed to the surface of the metal magnetic powder. In the metal magnetic powder to which the surface-active agent is adsorbed, the hydrophobic group or the polar group of the surface-active agent interacts with a bonding agent, and it displays a high dispersion property with reference to the bonding agent. Consequently, even when, e.g. a fine metal magnetic powder having a long-axis length of 0.2μm or lower is used, the metal magnetic powder is dispersed into the magnetic layer, and a good electromagnetic conversion characteristic is obtained in a high-density recording region.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer coating type magnetic recording medium, and more particularly to an improvement in dispersibility of a powder component in an upper layer and a lower layer.

[0002]

2. Description of the Related Art As a magnetic recording medium, a magnetic layer formed by dispersing a ferromagnetic powder, a binder, and various additives together with an organic solvent onto a non-magnetic support is dried to form a magnetic layer. A so-called coating type magnetic recording medium is known.

[0003] The coating type magnetic recording medium is widely used as a magnetic tape for audio or video, a data cartridge for backup, a floppy disk and the like. Such coating-type magnetic recording media are required to have higher recording density in order to cope with recent shortening of recording wavelength and digitization of recording method, and have more excellent electromagnetic conversion characteristics. Is required.

[0004] As a technique for improving the electromagnetic conversion characteristics of a magnetic recording medium, there is a method of first reducing the thickness of a magnetic layer. By reducing the thickness of the magnetic layer, self-demagnetization loss during recording is reduced,
Electromagnetic conversion characteristics are improved.

However, when a thin magnetic layer having a thickness of, for example, 0.5 μm or less is directly provided on the nonmagnetic support, the surface shape of the nonmagnetic support tends to appear on the surface of the magnetic layer, and the surface of the magnetic layer is smoothed. Becomes difficult. For this reason, in the case where the magnetic layer is thinned, a multi-layer coating type configuration in which a non-magnetic coating layer is interposed between the non-magnetic support and the magnetic layer is often adopted. By interposing the non-magnetic layer in this way, a thickness is obtained between the surface of the non-magnetic support and the surface of the magnetic layer, and the surface shape of the non-magnetic support is less likely to appear on the surface of the magnetic layer. Therefore, a thin magnetic layer is formed with a smooth surface shape.

As a method of forming such two coating layers on a non-magnetic support, a die head having two slits through which a non-magnetic paint and a magnetic paint are extruded, respectively, is used. A simultaneous multilayer coating method (wet-on-wet coating method) in which a nonmagnetic paint and a magnetic paint are simultaneously applied has been proposed.
In this simultaneous multilayer coating method, a coating film having a uniform thickness with few coating defects and coating streaks can be formed. Therefore, a medium with excellent electromagnetic conversion characteristics and low noise can be obtained. Further, the formed lower layer and upper layer have high adhesion, and excellent durability can be obtained.

Although the electromagnetic conversion characteristics of the magnetic recording medium are improved by reducing the thickness of the magnetic layer as described above, smoothing of the magnetic layer surface and improvement of the metal magnetic powder are also effective methods for improving the electromagnetic conversion characteristics. .

For example, the surface of the magnetic layer is generally smoothed for the purpose of minimizing the spacing loss during recording and reproduction. Particularly, in high-density recording, since the recording wavelength used is short, the recording and reproduction are easily affected by the roughness of the magnetic layer surface, and control of this surface roughness is particularly important.

Further, as an improvement of the ferromagnetic powder, (1)
Use of ferromagnetic alloy powder, (2) miniaturization of ferromagnetic powder,
(3) Increasing the coercive force of the ferromagnetic powder and making the coercive force distribution uniform.

As for (1) and (2), as a result of aggressive improvement of magnetic materials, ferromagnetic powders having a saturation magnetization of more than 140 Am ² / kg and a major axis length of 0.1 μm or less are now available. Have been developed.

Regarding the coercive force improvement of (3), a ferromagnetic powder having a coercive force exceeding 160 kA / m has been found, and the particle size distribution is reflected in the coercive force distribution of the ferromagnetic powder. However, the coercive force distribution is extremely uniform due to the uniformity of the particle size distribution.

[0012]

In order for a magnetic recording medium to exhibit good electromagnetic conversion characteristics, it is necessary that the ferromagnetic powder is uniformly dispersed in a binder. If the micronization of the ferromagnetic powder proceeds too much, it tends to be difficult to disperse the ferromagnetic powder in the binder.

As a countermeasure for this, it is conceivable to first extend the time required for kneading or dispersing at the stage of preparing the magnetic paint. However, if the kneading or dispersing time is increased, the magnetic powder is damaged, and the major axis length and the particle size distribution become non-uniform. Further, there is a problem that the manufacturing efficiency is reduced.

On the other hand, as a method for improving the dispersibility of the ferromagnetic powder, -SO ₃ M, -OSO ₃
M, -COOM, -P = O ( OM) 2, -NR 1 R 2, -
NR ₁ R ₂ R ₃ ⁺ X ⁻ ,> NR ₁ R ₂ ⁺ X ⁻ (where M represents a hydrogen atom or an alkali metal such as lithium, potassium, and sodium, and R ₁ , R ₂ , and R ₃ represent a hydrogen atom or . a hydrocarbon group also, X ^- interaction fluorine, chlorine, bromine, by introducing a polar functional group of the halogen element represents an ionic or an inorganic or organic ions) such as iodine, a ferromagnetic powder and a binder Attempts have been made to strengthen. However, although the introduction of polar functional groups into the binder does improve the dispersibility of the ferromagnetic powder, it is not sufficiently satisfactory. 0.2μ long axis developed for high density recording
In order to use an extremely fine ferromagnetic powder having a particle size of m or less, it is necessary to further study the dispersibility.

Accordingly, the present invention has been proposed in view of such a conventional situation, and is a multilayer coating type in which an upper magnetic layer is formed on a lower nonmagnetic layer, and has a fine ferromagnetic powder. It is an object of the present invention to provide a magnetic recording medium in which this ferromagnetic powder is highly dispersed in the upper magnetic layer even when the magnetic recording medium is used.

[0016]

In order to achieve the above-mentioned object, a magnetic recording medium of the present invention comprises a non-magnetic support in which a non-magnetic paint comprising a non-magnetic powder, a binder and an organic solvent is applied. After forming the lower non-magnetic layer by that, while the lower non-magnetic layer is in an undried state, the upper magnetic layer is formed by applying a magnetic paint comprising a metal magnetic powder, a binder and an organic solvent, The average thickness of the upper magnetic layer is 0.5 μm.
m or less, and the upper magnetic layer contains at least one of a surfactant represented by Chemical Formula 3 or an organic amine salt of a surfactant represented by Chemical Formula 3. is there.

[0017]

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In a multilayer coating type magnetic recording medium, if the thickness of the upper magnetic layer is regulated to 0.5 μm or less, the self-demagnetization loss during recording can be suppressed.

Further, when a surfactant represented by the chemical formula (3) or an organic amine salt of the surfactant represented by the chemical formula (3) is added to the upper magnetic layer, fine particles having a major axis length of 0.2 μm or less can be obtained as metal magnetic powder. Even when a fine powder is used, the metal magnetic powder is highly dispersed in the upper magnetic layer.

Therefore, this magnetic recording medium has a high output in a short-wave recording area and has excellent overwrite characteristics.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the magnetic recording medium according to the present invention will be described below.

FIG. 1 shows a magnetic recording medium to which the present invention is applied.
As shown in (1), after a lower non-magnetic layer 2 is formed by applying a non-magnetic paint composed of a non-magnetic powder, a binder and an organic solvent on a non-magnetic support 1, the lower non-magnetic layer 2 is uncoated. This is a multilayer coating type magnetic recording medium in which the upper magnetic layer 3 is formed by applying a magnetic paint comprising a metal magnetic powder, a binder and an organic solvent while it is in a dry state.

In the present invention, a surfactant (polyoxyethylene alkyl ether phosphate, polyoxyethylene alkyl allyl ether) represented by the following formula (4) is added to the upper magnetic layer 3 of such a multilayer coating type magnetic recording medium. Or an organic amine salt of a surfactant represented by Chemical formula 4.

[0024]

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When a surfactant having such a structure is contained in the upper magnetic layer 3, the hydroxyl group of the surfactant interacts with the surface of the metal magnetic powder, and the surfactant is adsorbed on the surface of the metal magnetic powder. The metal magnetic powder to which the surfactant is adsorbed exhibits high dispersibility in the binder because the hydrophobic group and the polar group of the surfactant interact with the binder.
Therefore, for example, even when a fine metal magnetic powder having a major axis length of 0.2 μm or less is used, the metal magnetic powder is highly dispersed in the magnetic layer, and good electromagnetic conversion characteristics can be obtained in a high-density recording region. .

Specific examples of the surfactant represented by Chemical Formula 4 include those represented by Chemical Formula 5, Chemical Formula 6, and Chemical Formula 7.

[0027]

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[0028]

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[0029]

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As the organic amine salt of the surfactant represented by Chemical Formula 4, for example, the one represented by Chemical Formula 8 is used.

[0031]

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These surfactants may be added alone or in combination of two or more.

In order to incorporate this surfactant into the upper magnetic layer 3, the surfactant is mixed with another coating composition at the stage of preparing the magnetic coating material, or the surface of the metal magnetic powder is added to the surface of the surfactant in advance. And the metal magnetic powder subjected to this treatment may be used for preparing a paint.

The amount of these surfactants contained in the upper magnetic layer 3 is 0.5 to 100 parts by weight of the metal magnetic powder.
5 parts by weight are suitable. When the amount of the surfactant is below this range, the dispersibility of the metal magnetic powder cannot be sufficiently improved. If the amount of the surfactant exceeds this range, a large amount of unreacted hydroxyl groups not interacting with the metal magnetic powder or the binder will remain, and these hydroxyl groups will interact with each other. In addition, the dispersibility of the metal magnetic powder decreases.

The above-mentioned surfactant is contained in the upper magnetic layer 3, and the following materials are used as other materials of the upper magnetic layer 3.

First, as the metal magnetic powder, Fe, C
o, metals such as Ni, Fe-Co, Fe-Ni, Fe-A
1, Fe-Ni-Al, Fe-Al-P, Fe-Ni-
Si-Al, Fe-Ni-Si-Al-Mn, Fe-M
n-Zn, Fe-Ni-Zn, Co-Ni, Co-P,
Fe-Co-Ni, Fe-Co-Ni-Cr, Fe-C
o-Ni-P, Fe-Co-B, Fe-Co-Cr-
An alloy of B, Mn-Bi, Mn-Al, Fe-Co-V, or the like is used. In addition, these metal magnetic powders are used for the purpose of preventing sintering during reduction or maintaining the shape.
Light metal elements such as Al, Si, P, and B may be contained in an appropriate amount. One type of these metal magnetic powders may be used alone, or a plurality of types may be used in combination.

The specific surface area, major axis length, and axial ratio of the metal magnetic powder are desirably within the following ranges.

First, the specific surface area of the metal magnetic powder is 30 to 8
Is preferably from 0 m ² / g, and more preferably 40~70m ² / g. The fact that the specific surface area is within the above range indicates that the powder shape is fine, high-density recording is possible, and excellent noise characteristics are obtained.

The major axis length is desirably 0.2 μm or less. When the major axis length of the metal magnetic powder exceeds 0.2 μm, there is a possibility that noise characteristics may be deteriorated. Also, the lower limit of the major axis length is 0.05 μm, and if the major axis length is less than this,
It becomes difficult to disperse the metal magnetic powder in the magnetic paint.

The axial ratio of the metal magnetic powder is 2 to 1.
5 is desirable. If the axial ratio is less than 2, the orientation of the metal magnetic powder is impaired, leading to a reduction in output. If the axial ratio exceeds 15, the signal output in the short wavelength region may be reduced.

The major axis length and axial ratio of the metal magnetic powder are determined by randomly selecting at least 100 samples from a transmission electron micrograph and calculating the average value.

Next, as the binder, a known thermoplastic resin conventionally used as a binder for a magnetic recording medium,
Thermosetting resins, reactive resins and the like are used, and those having a number average molecular weight of 5,000 to 100,000 are particularly preferable.

Examples of the thermoplastic resin include vinyl chloride, vinyl acetate, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylate-acrylonitrile copolymer, Acrylate-vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylate-acrylonitrile copolymer,
Acrylate-vinylidene chloride copolymer, methacrylate-vinylidene chloride copolymer, methacrylate-vinyl chloride copolymer, methacrylate-ethylene copolymer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer , Acrylonitrile-
Butadiene copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose), styrene butadiene copolymer, polyurethane resin, polyester resin, amino resin, And synthetic rubber.

The thermosetting resin or the reactive resin includes a phenol resin, an epoxy resin, a polyurethane curing resin, a urea resin, a melamine resin, an alkyd resin,
Silicone resins, polyamine resins, urea-formaldehyde resins and the like can also be used.

All of the above binders include -SO ₃ M and -OSO ₃ for the purpose of improving the dispersibility of the metal magnetic powder.
M, -COOM, P = O ( OM) 2 ( where, M in the formula represents an alkali metal such as a hydrogen atom or a lithium, potassium, sodium) _{or, -NR 1 R 2, -NR 1} R 2 R 3 + X
^- side chain amine having terminal ^{_{groups,> NR 1 R 2 + X}} - main-chain amine represented by (wherein, wherein R _1, R _2, R ₃ represents a hydrogen atom or a hydrocarbon group, X ^- is fluorine, chlorine,
Represents a halogen element ion such as bromine or iodine or an inorganic ion or an organic ion), and further represents -OH, -SH, -C
A polar functional group such as N or an epoxy group may be introduced. The amount of these polar functional groups introduced into the binder is 10 ⁻⁸ to
It is preferably 10 ^-1 mol / g, and 10 ^-6 to 10 ^-2.
More preferably, it is mol / g. Note that these binders may be used alone or in combination of two or more.

The amount of the binder used in the upper magnetic layer 3 is preferably 1 to 200 parts by weight, more preferably 10 to 50 parts by weight, based on 100 parts by weight of the metal magnetic powder. If the binder is used in a larger amount than this range, the output of the magnetic layer is reduced because the amount of the metal magnetic powder contained in the magnetic layer is relatively small. Further, when the magnetic layer is repeatedly slid on the drive device, the magnetic layer is liable to cause plastic flow, and the running durability is deteriorated. On the other hand, when the binder is used in an amount smaller than the above range, the magnetic layer becomes brittle and sufficient running durability cannot be obtained.

As a solvent used for coating, acetone,
Methyl ethyl ketone, methyl isobutyl ketone, ketone solvents such as cyclohexanone, alcohol solvents such as methanol, ethanol, propanol, methyl acetate,
Ethyl acetate, butyl acetate, propyl acetate, ethyl lactate,
Ester solvents such as ethylene glycol acetate, diethylene glycol dimethyl ether, 2-ethoxyethanol, ether solvents such as tetrahydrofuran and dioxane, benzene, toluene, aromatic hydrocarbon solvents such as xylene, methylene chloride, ethylene chloride, carbon tetrachloride, Halogenated hydrocarbon solvents such as chloroform and chlorobenzene are used.

The magnetic paint is a metal magnetic powder as described above,
It is prepared by kneading, mixing and dispersing a binder and an organic solvent. As the kneading and dispersing device, a roll mill,
A ball mill, a sand mill, an agitator, a kneader, an extruder, a homogenizer, an ultrasonic disperser and the like are used.

On the other hand, the following materials are used as the material of the lower nonmagnetic layer 2.

First, as the nonmagnetic powder, α-Fe ₂ O ₃
Such as non-magnetic iron oxide, goethite, rutile type titanium oxide,
Anatase type titanium oxide, tin oxide, tungsten oxide,
Silicon oxide, zinc oxide, chromium oxide, cerium oxide, titanium carbide, BN, α-alumina, β-alumina, γ
-Alumina, calcium sulfate, barium sulfate, molybdenum disulfide, magnesium carbonate, calcium carbonate, barium carbonate, strontium carbonate, barium titanate and the like. These non-magnetic powders may be doped with an appropriate amount of impurities depending on the purpose. For the purpose of improving dispersibility, imparting conductivity, and improving color tone, Al, S
The surface treatment may be performed with a compound containing i, Ti, Sn, Sb, Zr, or the like. The specific surface area of these nonmagnetic powders is preferably 30 to 80 m ² / g,
More preferably, it is 40 to 70 m ² / g. These non-magnetic powders may be used alone or in combination of two or more.

The nonmagnetic powder may contain carbon black such as furnace black for rubber, pyrolytic carbon, black for color, and acetylene black, if necessary. These carbon blacks have a specific surface area of 100
400 m ² / g, DBP oil absorption 20-200 ml /
Preferably, it is 100 g.

The specific surface areas of carbon black and other non-magnetic powders are set in the above-mentioned range because the surface of the upper magnetic layer 3 is smoothed, the modulation noise characteristics are improved, and the influence of spacing loss is improved. It is to suppress.

That is, in a multilayer coating type magnetic recording medium in which the upper magnetic layer 3 is formed with a very small thickness, the surface property of the lower non-magnetic layer is remarkably reflected on the upper magnetic layer 3. Therefore, in order to smooth the surface of the upper magnetic layer 3, it is necessary that the lower non-magnetic layer is formed smoothly.

Here, the fact that the specific surface area of the non-magnetic powder contained in the lower non-magnetic layer 2 is not less than the lower limit of the above range indicates that the powder is fine, and that the surface of the lower non-magnetic layer The shape of this non-magnetic powder is difficult to appear. Therefore, the lower non-magnetic layer 2 is formed to have a smooth surface, and the upper magnetic layer 3 is also made to have a smooth surface in accordance with this.

However, since the non-magnetic powder has no magnetic cohesive force, the dispersibility is less likely to be reduced due to miniaturization as compared with the magnetic powder. Becomes difficult. As a result, the surface smoothness of the lower non-magnetic layer 2 and thus the upper magnetic layer 3 is impaired,
Sufficient electromagnetic conversion characteristics cannot be obtained in a high-density recording area.

As the binder and the organic solvent for the lower non-magnetic layer 2, any of those exemplified for the upper magnetic layer 3 can be used. The amount of the binder used in the lower non-magnetic layer 2 is
The amount is preferably 1 to 200 parts by weight, more preferably 10 to 50 parts by weight, based on 100 parts by weight of the nonmagnetic powder. If the binder is used in a larger amount than this range,
When the medium is repeatedly slid on the drive device, the non-magnetic layer easily causes plastic flow, and the running durability is deteriorated. On the other hand, when the binder is used in an amount smaller than the above range, the nonmagnetic layer becomes brittle, and sufficient running durability cannot be obtained.

Further, to the lower non-magnetic layer 2, at least one of the surfactant represented by Chemical Formula 4 or the amine salt of the surfactant represented by Chemical Formula 4 to be added to the upper magnetic layer 3 is added. You may do it. When a surfactant having such a structure is contained in the lower nonmagnetic layer 2, the hydroxyl groups of the surfactant interact with the surface of the nonmagnetic powder, and the surfactant is adsorbed on the surface of the nonmagnetic powder. By the action of the surfactant, the nonmagnetic powder is highly dispersed in the binder, and the lower nonmagnetic layer 2 and, consequently, the upper magnetic layer 3 can be formed to have a smoother surface.

In this case, the surfactant may be added alone or in combination of two or more.

In order to make the lower non-magnetic layer 2 contain a surfactant, the surfactant is mixed with another coating composition at the stage of preparing the non-magnetic coating, or the surface of the non-magnetic powder is prepared in advance. The treatment may be carried out with a surfactant, and the non-magnetic powder thus treated may be used for preparing a paint.

The amount of these surfactants to be contained in the nonmagnetic layer is suitably 0.5 to 5 parts by weight based on 100 parts by weight of the nonmagnetic powder. When the amount of the surfactant is below this range, the dispersibility of the non-magnetic powder cannot be sufficiently improved. If the amount of the surfactant exceeds this range, a large amount of unreacted hydroxyl groups not interacting with the non-magnetic powder and the binder will remain, and these hydroxyl groups will interact with each other. In addition, the dispersibility of the non-magnetic powder decreases.

The non-magnetic paint is a non-magnetic powder as described above,
It is prepared by kneading, mixing and dispersing a binder and an organic solvent. As the kneading and dispersing device, any of those exemplified for the upper magnetic layer 3 can be used.

The upper magnetic coating and the lower non-magnetic coating prepared from the above-mentioned materials are coated on a non-magnetic support 1 and dried to form an upper magnetic layer 3 and a lower non-magnetic layer 2.

The nonmagnetic support 1 is represented by polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, celluloses such as cellulose triacetate and cellulose diacetate, vinyl resins, polyimides and polycarbonates. A support made of such a polymer material, metal, glass, ceramics, or the like is used.

The prepared two kinds of paints were applied to a non-magnetic support 1
For application on the upper layer, a so-called wet-on-wet coating method (wet multilayer coating method) is used, in which an upper layer coating is overlaid on a lower layer coating in a wet state.

FIG. 1 shows an example of a coating apparatus for applying a paint by the wet-on-wet coating method.

This coating apparatus has two slits (a slit 11 for a lower layer paint,
Die head 18 having slit 12) for upper paint
(4 lip type die head). That is, in this die head, the two slit portions 11, 1
A lower paint reservoir 13 and an upper paint reservoir 14 to which a lower paint and an upper paint are supplied, respectively, are formed on the back side of 2.
The lower layer paint and the upper layer paint supplied to the paint pools 13 and 14 are extruded through the slits 11 and 12 to the tip of the die head. On the other hand, the support 1 to which the paint is applied
Travels in the direction A in the figure from the slit 11 for the lower layer paint to the slit 12 for the upper layer paint along the tip surface of the die head.

When the non-magnetic support 1 running in this way first passes through the slit 11 for the lower layer paint,
The lower layer paint extruded from the slit portion 11 is applied to the surface to form a lower layer coating film 16. Then, when passing through the slit 12 for the upper layer paint, the slit 1
The upper coating material extruded from the lower coating film 16 is in a wet state of the lower coating film 16.
Is applied thereon to form two coatings 16,17. Then, the two-layered coating film in a wet state is dried and subjected to a surface smoothing treatment such as a calendering treatment as necessary, whereby a multilayer coating type magnetic recording medium is produced.

As the die head, besides the four-lip method, there are also a three-lip method and a two-lip method.

Since the lower layer and the upper layer formed by the wet-on-wet coating method are formed by applying the upper layer paint on the wet lower layer coating film, the surface of the lower layer, that is, The boundary between the lower layer and the upper layer is formed smoothly. Therefore, the surface properties of the upper layer are also very good, dropout is suppressed, high output,
It is suitable for high density recording where low noise is strictly required. Further, since the adhesion between the lower layer and the upper layer is high, film peeling hardly occurs and excellent durability can be obtained.

A clear boundary substantially exists between the lower layer and the upper layer formed by the wet-on-wet coating method, and a boundary in which the components of both layers are mixed with a certain thickness. There may be regions. In the present invention, when such a boundary region exists, a layer below the boundary region is defined as a lower layer and an upper layer is defined as an upper layer except for the boundary region.

The lower non-magnetic layer 2 and the upper magnetic layer 3 are formed in this manner.
Is regulated to 0.5 μm or less after calendering. By setting the thickness of the upper magnetic layer 3 to 0.5 μm or less, the self-demagnetization loss during recording is suppressed, the output in the short wavelength region is increased, and the overwrite characteristics are improved.

The basic structure of the magnetic recording medium of the present invention has been described above. This magnetic recording medium is characterized by having an additional structure usually used for a multilayer coating type magnetic recording medium. May be improved.

For example, additives such as a lubricant and abrasive particles may be added to the upper magnetic layer 3 and the lower nonmagnetic layer 2 as necessary.

Examples of the lubricant include solid lubricants such as graphite, molybdenum disulfide and tungsten disulfide, silicone oil, fatty acids having 10 to 22 carbon atoms, and 10 to 22 carbon atoms.
Fatty acid esters, terpene-based compounds, and oligomers thereof, which are synthesized from the above-mentioned fatty acids and alcohols having 2 to 26 carbon atoms. These lubricants may be added only to the upper layer, or may be added to both the upper layer and the lower layer.

The abrasive particles are added to the upper magnetic layer 3 and include, for example, aluminum oxide (α, β, γ), chromium oxide, silicon carbide, diamond, garnet, emery,
Boron nitride, titanium carbide, silicon carbide, titanium carbide, titanium oxide (rutile type, anatase type) and the like are used.

These abrasive particles have a Mohs altitude of 4 or more, preferably 5 or more, and a specific gravity of 2 to 2.
6, preferably in the range of 3-5. Further, the average particle size is preferably 0.5 μm or less, and more preferably 0.3 μm or less. The average particle size of the abrasive particles is also determined by randomly selecting 100 or more samples from a transmission electron micrograph and calculating the average value.

The amount of these abrasive particles added to the upper magnetic layer 3 is preferably not more than 20 parts by weight, more preferably not more than 10 parts by weight based on 100 parts by weight of the metal magnetic powder.

Further, a polyisocyanate for crosslinking and curing the binder may be used in combination to increase the strength of the coating film. As this polyisocyanate, toluene diisocyanate and its adduct, alkylene diisocyanate, and their adducts can be used. The addition amount of these polyisocyanates is
5 to 80 parts by weight, preferably 10 to 5 parts by weight per 0 parts by weight
0 parts by weight is suitable. This polyisocyanate is
It may be used for both upper and lower layers, or may be used for only the upper layer. When used in both upper and lower layers, the amount may be equal in each layer or may be changed at an arbitrary ratio.

Further, the magnetic recording medium is provided on the surface opposite to the side on which the upper and lower layers of the non-magnetic support 1 are formed, with the aim of improving running properties, preventing electrification, preventing transfer, and the like.
A back coat layer may be provided. Further, an undercoat layer may be provided between the lower layer and the non-magnetic support 1 for the purpose of enhancing the adhesion between the lower layer and the support.

[0080]

Embodiments of the present invention will be described below based on experimental results.

Example 1 First, an upper layer paint was prepared based on the following composition. Paint is made according to the usual method, metal magnetic powder, binder, additive,
After mixing the solvent and the surfactant, the mixture was kneaded with an extruder, and further dispersed by a sand mill for 6 hours.

Upper layer coating composition Fe-based metal ferromagnetic powder 100 parts by weight (coercive force: 160 kA / m, saturation magnetization: 145 Am ² / kg, specific surface area: 51 m ² / g, major axis length: 0.08 μm, needle Shape ratio: 3) Polyvinyl chloride resin 14 parts by weight (containing potassium sulfonate as a polar group, manufactured by Nippon Zeon Co., Ltd., trade name: MR-110) Polyester polyurethane resin 3 parts by weight (containing sodium sulfonate as a polar group, manufactured by Toyobo Co., Ltd.) Additive: Al ₂ O ₃ 5 parts by weight Surfactant 1 part by weight stearic acid 1 part by weight heptyl stearate 1 part by weight Methyl ethylene ketone 150 parts by weight Cyclohexanone 150 parts by weight The surfactants are the anionic surfactants shown in Table 1. The surfactant was added in the amounts shown in the same table.

Next, a lower layer paint was prepared based on the following composition. The coating was performed by mixing a non-magnetic powder, a binder, an additive, a solvent, and a surfactant, kneading with an extruder, and further dispersing with a sand mill for 6 hours according to a conventional method.

Lower layer coating composition Acicular α-Fe ₂ O ₃ 100 parts by weight (specific surface area: 53 m ² / g, major axis length: 0.15 μm, acicular ratio: 5) Polyvinyl chloride resin 13 parts by weight (polar group) 4% by weight of polyester polyurethane resin (manufactured by Toyobo Co., Ltd. containing sodium sulfonate as a polar group) Additive: 1 part by weight of stearic acid 1 part by weight of heptyl stearate 1 part by weight of methyl ethyl ketone 105 parts by weight Cyclohexanone 105 parts by weight After adding 3 parts by weight of polyisocyanate to each of the prepared upper layer paint and lower layer paint, these paints were added to 4 parts by weight.
Using a lip-type die coater, simultaneous multi-layer coating was performed on a 7 μm-thick polyethylene terephthalate film. Then, in an undried state, the upper coating film was subjected to an orientation treatment using a solenoid coil, and then dried, calendered, and cured to form an upper magnetic layer and a lower nonmagnetic layer. The coating thickness of each layer is 0.2 μm for the upper layer and 2.0 μm for the lower layer after calendering.

On the other hand, a back coating was prepared based on the following composition.

Composition of Back Coating Carbon black (trade name Asahi # 80) 100 parts by weight Polyester polyurethane (trade name Nipporan N-2304) 100 parts by weight Methyl ethyl ketone 500 parts by weight Toluene 500 parts by weight A back coat layer was formed by applying on the surface opposite to the side on which the upper layer and the lower layer were formed.

Then, the raw tape on which the upper layer, the lower layer, and the back coat layer were formed was formed into a tape by slitting the tape to a width of 8 mm.

Examples 2 to 4 The same procedures as in Example 1 were carried out except that the surfactant having the structure shown in Table 1 was used as the surfactant to be added to the upper layer paint, and this surfactant was added in the amount shown in the table. Similarly, a magnetic tape was produced.

Examples 5 to 8 Surfactants having the structure shown in Table 2 were used as the surfactants to be added to the upper coating composition. A magnetic tape was produced in the same manner as in Example 1 except that the surfactant having the structure shown in Table 1 was added in the amount shown in the same table.

Comparative Example 1 Example 1 except that no surfactant was added to the upper layer paint.
A magnetic tape was produced in the same manner as described above.

[0091]

[Table 1]

[0092]

[Table 2]

The magnetic conversion characteristics and the surface roughness Ra of the magnetic tape thus manufactured were measured.

The measurement of the electromagnetic conversion characteristics was performed using a fixed head type electromagnetic conversion characteristic measuring device. This measuring machine
It has a rotating drum and a head that contacts the rotating drum, and a magnetic tape is wound around the drum. On this measuring machine,
First, a 10 MHz rectangular wave signal was recorded on each magnetic tape at an optimum recording current, and then a 10 MHz output level was detected by a spectrum analyzer. The relative speed between the tape and the head was set at 3.33 m / s. Also,
The values of the electromagnetic conversion characteristics were expressed as relative values when an 8 mm Hi8 tape manufactured by Sony Corporation was used as a reference tape, and the output level of the reference tape was 0 dB.

The surface roughness Ra is JIS B060
The center line average roughness Ra specified in 1 was measured using a non-contact type surface roughness meter based on a laser light interference method.

Table 3 shows the results of these measurements.

[0097]

[Table 3]

As shown in Table 3, the magnetic tapes of Examples 1 to 4 in which a surfactant having a predetermined structure was added to the upper magnetic layer, and both the upper magnetic layer and the lower non-magnetic layer had the predetermined structure. 5 to 8 in which a surfactant having a surfactant was added.
The magnetic tape has a lower surface roughness Ra than Comparative Example 1 in which no surfactant is added to any of the upper and lower layers, and a large reproduction output is obtained. In particular, in a system in which a surfactant is added to both the upper layer and the lower layer, the surface roughness Ra is lower than in a system in which a surfactant is added to only the upper layer, and the reproduction output tends to be higher.

Thus, adding a surfactant having a predetermined structure to the upper magnetic layer, and further to both the upper magnetic layer and the lower non-magnetic layer, improves the surface smoothness of the upper magnetic layer and improves the electromagnetic conversion characteristics. Has been found to be effective in improving.

Examination of the amount of surfactant added 1 A magnetic tape was produced in the same manner as in Example 1 except that the amount of surfactant added to the upper magnetic layer was changed as shown in Table 4. Examples 1 to 5).

[0101]

[Table 4]

The magnetic conversion characteristics and the surface roughness Ra of the produced magnetic tape were measured in the same manner as described above. Table 5 shows the measurement results.

[0103]

[Table 5]

As shown in Table 5, when the amount of the surfactant added to the upper magnetic layer was 0.1 part by weight, the surface roughness Ra could not be sufficiently reduced, and the reproduction output was lower than that of Comparative Example 1. Not much different from tape. When the amount of the surfactant added to the upper magnetic layer is in the range of 0.5 to 5 parts by weight, the surface roughness Ra decreases as the amount of the surfactant increases, and the reproduction output increases. Further, when the addition amount of the surfactant is 6 parts by weight, the surface roughness Ra increases, and the reproduction output decreases.

As described above, the amount of the surfactant to be added to the upper magnetic layer is 0.5 to 100 parts by weight of the metal magnetic powder.
It has been found that it is appropriate to use up to 5 parts by weight.

Investigation of the amount of surfactant added 2 A surfactant having the structure shown in Table 6 was used as the surfactant to be added to the upper layer paint, and this surfactant was added in the amount shown in the same table and added to the lower layer paint. Magnetic tapes were produced in the same manner as in Example 1 except that the surfactant having the structure shown in Table 6 was added in the amount shown in Table 6 (Experimental Examples 6 to 9).

[0107]

[Table 6]

The magnetic conversion characteristics and the surface roughness Ra of the produced magnetic tape were measured in the same manner as described above. Table 7 shows the measurement results.

[0109]

[Table 7]

As shown in Table 7, the magnetic tapes of Experimental Examples 6 and 8 in which the amount of the surfactant added was 0.5 to 5 parts by weight for both the upper magnetic layer and the lower nonmagnetic layer, The surface roughness Ra is low, and a large reproduction output is obtained. On the other hand, the magnetic tapes of Experimental Examples 6 and 9 in which a surfactant was added to the upper magnetic layer or the lower non-magnetic layer in an amount exceeding 5 parts by weight had a high surface roughness Ra. , Playback output is small.

Thus, when a surfactant is added to both the upper magnetic layer and the lower non-magnetic layer, the amount of the surfactant added is 0.1 to 100 parts by weight of the metal magnetic powder or the non-magnetic powder. It has been found that the content should be 5 to 5 parts by weight.

[0112]

As is apparent from the above description, the magnetic recording medium of the present invention is a multi-layer coating type magnetic recording medium in which the thickness of the upper magnetic layer is regulated to 0.5 μm or less. Therefore, self-demagnetization loss during recording can be suppressed. In addition, since a surfactant having a predetermined structure is added to at least the upper magnetic layer, even when a relatively fine metal magnetic powder having a major axis length of 0.2 μm or less is used, this metal magnetic powder can be used as the upper magnetic layer. It can be highly dispersed in the layers. Therefore, good electromagnetic conversion characteristics can be obtained in a high density recording area.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a configuration example of a magnetic recording medium to which the present invention is applied.

FIG. 2 is a schematic diagram showing an application device for applying a lower layer paint and an upper layer paint.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Non-magnetic support 2 Lower non-magnetic layer 3 Upper magnetic layer

Claims (6)

[Claims] 1. A non-magnetic paint comprising a non-magnetic powder, a binder and an organic solvent is applied on a non-magnetic support to form a lower non-magnetic layer, and the lower non-magnetic layer is dried in an undried state. Meanwhile, the upper magnetic layer is formed by applying a magnetic paint composed of a metal magnetic powder, a binder and an organic solvent,
In the magnetic recording medium in which the average thickness of the upper magnetic layer is 0.5 μm or less, the upper magnetic layer may include at least one of a surfactant represented by Chemical Formula 1 or an organic amine salt of a surfactant represented by Chemical Formula 1. A magnetic recording medium comprising: Embedded image 2. The long axis length of the metal magnetic powder is 0.20 μm.
2. The magnetic recording medium according to claim 1, wherein: 3. The magnetic recording medium according to claim 1, wherein the content of the surfactant in the upper magnetic layer is 0.5 to 5 parts by weight based on 100 parts by weight of the metal magnetic powder. 4. The magnetic recording medium according to claim 1, wherein the binder of the upper magnetic layer contains a polar group. 5. The lower nonmagnetic layer contains at least one of a surfactant represented by Chemical Formula 2 and an organic amine salt of a surfactant represented by Chemical Formula 2. Magnetic recording medium. Embedded image 6. The magnetic recording medium according to claim 5, wherein the content of the surfactant in the lower nonmagnetic layer is 0.5 to 5 parts by weight based on 100 parts by weight of the nonmagnetic powder. .